Question 342066
A manufacturer claims that the mean lifetime,u , of its light bulbs is 51 months. The standard deviation of these lifetimes is 7 months. 
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Sixty bulbs are selected at random, and their mean lifetime is found to be 53 months.
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 Can we conclude, at the 0.1 level of significance, that the mean lifetime of light bulbs made by this manufacturer differs from 51 months?
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Perform a two-tailed test. 
Then fill in the table below. 
Carry your intermediate computations to at least three decimal places, and round your responses as specified in the table. (If necessary, consult a list of formulas.) 
the null hypothesis: u = 51
The alternative hypothesis: u is not equal to 51
The type of test statistic (choose Z, t, Chi-square, or F)
The value of the test statistic (round to at least three decimal places:
t = (53-51)/[7/sqrt(60)] = 2.213
Can we conclude that the mean lifetime of the bulbs made by this manufacture differ from 51 months?
p-value = 2*P(t > 2.213 when dr = 59) = 2*tcdf(2.213,100,59) = 2*0.0154
= 0.0308
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Since the p-value is greater than 1%, fail to reject Ho.
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Cheers,
Stan H.